Effects of dopaminergic stimulants on cyclic nucleotide levels in mouse brain in vivo.

Dopaminergic stimulants (amantadine, amphetamine, apomorphine, nomifensine and L-dopa plus benserazide) increased cyclic GMP levels in the medial forebrain and cerebellum of mice. Cyclic AMP levels were not significantly altered under these conditions. Drug-induced stereotyped behaviour correlated in intensity and duration to the changes in cyclic GMP levels in the medial forebrain. Amantadine, apomorphine and nomifensine showed a linear dose response relationship, but differed as to the extent and time course of the increase in cyclic GMP. Amantadine and apomorphine were were more effective in elevating cyclic GMP in the medial forebrain than in the cerebellum. Amphetamine produced an exponential dose-related elevation of cyclic GMP in both parts of the brain, being more effective in the cerebellum than in the medial forebrain at high doses, thus indicating a complex mechanism of action. L-Dopa (50 mg/kg) and benserazide (40 mg/kg) alone did neither significantly increase cyclic GMP levels nor induce stereotyped behaviour. However, in animals pretreated with benserazide (15 min prior to L-odopa) L-dopa produced a significant elevation of cyclic GMP and stereotyped behaviour.